1. Field of the Invention
The present invention relates to an apparatus for upgrading a computer system equipped with a digital signal processor to include modem and facsimile functions.
2. Description of the Related Art
Computer systems are generally designed to include an input/output (I/O) bus coupled to one or more connectors or slots to allow the computer system to be upgraded by adding optional capabilities. The optional capabilities or functions are typically incorporated onto a separate printed circuit board or option card. The option card includes a connector which plugs into a slot on the I/O bus to electrically couple the circuitry on the option card to the computer system. One such optional function is a sound board, such as the Soundblaster by Creative Labs, Inc., while another is a modem or fax/modem board. The Soundblaster option includes audio processing capability for interfacing the computer to a variety of peripherals and functions, such as a joystick and stereo sound for computer games, musical synthesis and a CD ROM.
At the heart of the sound board is often a powerful numeric processor, such as a digital signal processor (DSP), which can perform frequency modulation synthesis for the various functions of the sound board. The DSP typically performs signal processing used for a variety of multimedia applications, such as electronic data processing, high precision servo control, graphics various capabilities for work stations, robotics, image processing, process control, real time simulation and instrumentation, speech recognition and synthesis, and telecommunication capabilities such as PBX, modems and facsimiles (faxes). For purposes of simplification, modem functions discussed hereinafter are assumed to include the capability to handle fax information, since the communication protocol is similar.
High speed modem systems are also typically incorporated onto an option card and usually include a “data pump” for supporting the various protocols of modem communication, such as the V.22, V.22bis, V.32 and V.32bis protocols recommended by the International Telegraph and Telephone Consultative Committee (CCITT). The data pump itself typically includes a DSP for performing modulation, demodulation and echo cancellation and a coder-decoder (CODEC) for performing analog to digital (A/D) and digital to analog (D/A) conversion. Analog signals from the phone line are digitized by the CODEC, and then demodulated by the DSP to extract the original digital data sent by an external device. This procedure is reversed for data transmitted by the modem to the external device.
The data pump is coupled to the phone line through a data access arrangement (DAA), which electrically isolates the modem from the phone line to control emissions of electromagnetic interference/radio frequency interference (EMI/RFI) as required by the Federal Communications Commission (FCC). The DAA also typically isolates the received from the transmitted analog signals, and develops a digital ring signal to inform the computer system to answer. The DAA receives signals from the phone line through a telephone jack, such as an RJ11C used for standard telephones. Other support logic is typically included to interface the modem to the computer system, such as a microcontroller for establishing a communications link, controlling the sequence of events to originate or answer a call, and to transmit or receive digital data from the computer system through a universal asynchronous receiver transmitter (UART) across the I/O bus. The microcontroller also typically performs error correction procedures, such as according to the V.42 protocol recommended by the CCITT, as well as compression/decompression procedures, such as according to the V.42bis protocol recommended by the CCITT.
A significant disadvantage of the prior art option cards requiring complex numeric operations offered for computer systems is that a user must pay for multiple DSPs, one for each additional option. An integrated card incorporating multiple functions including a modem might appear to be desirable, but there are several disadvantages. First, even though only a single DSP would be required, a combination card would be more expensive than the cards in present use. Those persons requiring only audio functions would be forced to purchase the modem components, defeating the purpose of saving cost.
Furthermore, an integrated modem raises problems when shipping to foreign countries, such as Germany. An extensive qualification process is required for any modem shipped to a foreign country, which usually takes about six months to complete. The qualification process must be performed for any electrical device attachable to phone lines, such as modems, and includes anything electrically integrated to the modem. The qualification process must be performed again if any changes are made, including non-modem changes, to a device attached to the phone lines. Those persons in foreign countries only needing audio functions but forced to purchase an integrated modem would also be forced to wait until the qualification process was complete to use the new functions, even if they do not intend to use the modem.
It is therefore desirable to provide an optional modem apparatus to upgrade a computer system to include modem capability using a DSP already provided in the computer system or on an option card.